Lists and Strings

George Mason University

Today’s topics

• Review of Chapter 5: Lists and Strings• Go over examples and questions• lists and strings in Python

List (and strings) review

• How do we declare a list? An empty list?• What operations can we apply to lists?• How are lists represented in memory?– primitive types– complex types

• What happens when we assign a variable to a list? (in memory)

• What is a character?• How is a string similar to a list? Different?• What is the substring operation?

Let’s go over the exercises

Lists in python

• .append( ) is a way to add a single element to the end of a list

length in python

• len( ) is a function to return the length of a list or string

python memory visualizer

• let’s use the python memory visualizer to trace through an example:

http://pythontutor.com/visualize.html#code=x+%3D+1%0Asmall+%3D+%5Bx,+2,+3%5D%0Amedium+%3D+%5B43,+76,+180,+57%5D%0Alarge+%3D+%5B234%5D%0AbigList+%3D+%5Bmedium,+small,+large%5D%0Aprint+small%0Aprint+bigList%0Asmall%5B0%5D+%3D+-1%0Aprint+small%0Aprint+bigList%0Ax+%3D+7%0Aprint+small&mode=display&cumulative=false&heapPrimitives=false&drawParentPointers=false&textReferences=false&showOnlyOutputs=false&py=2&rawInputLstJSON=%5B%5D&curInstr=0

Note the difference between the storage of x, a primitive, and the lists.

Debugging with id( )

• id( ) can be used to print out the memory address of a complex type

• str( ) is needed to add non-strings to strings

Debugging with id( )

index( )

• Note you’ll need to check if the element is in the list or string before trying to get its index

in

• in is a keyword and can be used to check if the element is in the list or string before trying to get its index

substrings and sub-lists with [:]

newlines and tabs

Other useful functions

• min(list)• max(list)• list.remove(1.5)• sortedList = sorted(list)

Strings in Python

• ‘cat’ and “cat” are the same– can use single or double quote– default is single quote– useful for “’” versus ‘”’

Questions?